Treating drilling muds



Patented Dec. 30, 1947 =to Union Oil-Company of California, Los Angeles, vOallf., a corporation of California *No Drawing. "Original application February 114, ""1939, Serial No. 256,304, now Patent :No. 2,343,113, dated February 29, 1944. Dividedand rthis application July 13, 1943, --Serial ;No.

" 11 Claims. (01. 252- 815) '.'I'his ..inverition relates .to the chemical treatmentotmudssuc'has areemployed in'thedrilling o'f oil'wells, and "to the reclaiming of such muds which'have become contaminated with cement or -i s imilar. mat'erials. This application is a division of my co-pending application, Seria1 No."256,30I4 for Treatihg drillin'g mud,"fi1ed February T4, 1939, .which has .now matured into PatentrNo.f2f343,l'l3, "dated Feb. 29, 1944.

In .jgen'era'l, it "may he said thato muds, such as those employed infth'e drilling of oil ;wells, are

:colloid'al suspensions of clay "in water to'which other materials, such; as barium sulfate, may be "adde'diin order to increase. their apparent specific "gravity. The physical characteristics of @these 'clay suspensions are largely determined .by the properties of the individual clay particles, most im ortant of "which are size, shape and surface characteristics. Furthermore, it "is recognized that "cl'ay's, whic ccnsit' predommatiy of "hy- "drated silica'tes of alumina, when suspendedin "water, possess an appreciable electric charge, suchpharge in generalfb'in'g of a "negative character.

Until 'ne'ceiitly, afi as" been I considered that the "principal -functions =-'of a mud in drilling -0perations are three fold It should form a cake u'p'on "the wall -of the hole. It "shouldretain in suspen- "sion the -=cuttings forin'e'd so that the latter -may be removed fi-om' the "'hole along with the rnud, wind it shou-ld p'dssess suflicie'rit weight lt'o overcome airy ill ss'lll-e encountered during .1 drilling. Ihese fuh'ctions "are ndnside'red more detail -below.

:One o f the primary difficulties encountered .in "thefidrillingfiof wells is that due to .=the asloughing or caving ihtothe *hole of the formationslpena titrated. I RfiOILtO my discovery, the use offdrilling .lmuds wasacommonlyrsupposed' to lessen theatend- "encyafior'caving by'fmudding-ofi theformations, tthatris,::iorminga"cale on-.ithe wiallsvofithe hole.

I have now idis'covered that :muds which form a thick tough icaisewincrea-se the tendency for rjsloughing, t andrthatmuds that formu a s thinsg'elat- :inous :cakezare Ethefindst desirable.

.In order for drilling to pro'ce'edsmoothly, means must be provided for continuously removing the cuttings fromthe hole and to this end drilling mud is circulated through the hole. The mud must be of sufficieritly low viscosity to allow it ito-be readily pumpedand it should be thixotropic. Thixotropy is that property of colloidal suspension which .involves an increase in gel strength as a function of the time-6f quiescent standing. This property is valualiilein that it prevents, to allarge extent, the sedimentation of the cuttings inthe hole during periods of suspended circulation. 'Howeveniminediately after violent agitation,'such as is induced by the circulation of the mud, cuttings will settle a-short distance an'd this fact'is utilized for their removal in a settling tank ,lp'rovided for the "purpose and in which "the de- ,gree of agitation is suddenly "lowered to practi- "cally zero. I have found that a mud'which'ha s fpro'per iwall building characteristics and ispui ripable will havea'dequate thixotropic properties.

Obviously, the total weight of a mud must be sufficiently great to prevent blow-outs from any .hig'hpressure formations that may be encountered, butobeyond this point, the need for greater weight is 'problematical. A rapid reduction in the hydrostatic head maintained on formations, caused-by a reductio'ninthe weight of the "mud oorlby permitting the level of the mud'in the well to fall ,while removing the drilling tools "fromthe .hole may cause dangerous "caving. Therefore, mud isusually pumped into the well while removing the drill string in order to maintain a substantially constan't hydrostatic head on the for- Jmati'ons being drilled and the mud 'weig'ht'is *alwayslkept as constant'asjpractical. In general, thaprac'tice 'hasbeento keep the weightof mud only sufficiently high to-prevent blow-outs. It is commonpractice, to increase the specific gravity ofra-mud-by adding: insoluble materialsofhigh specific gravity, .such 7 as,. for example, ,bariu'mfsfiliate. Because of their insolubility, the usual weighting agents employed have little effect on t-the performance characteristicsof.a'mud. g

I have discovered that by employinga drilling mud which possesses a minimum tendency to lose water from the fiuid to the formation, a marked reduction in the caving of formations and consequent reduction in the sticking of drilling tools is realized. It has been found that the structural strengths of most formations which are penetrated during drilling are sufficient to prevent the walls of the hole from caving but that many such formations are considerably weakened when saturated with water and when so wet often slough into the hole. Frequently such action causes seizing of the drill pipe or tools so that they cannot be moved and costly fishing jobs result. It is, therefore, of the greatest importance to prevent loss of water from the drilling mud to the formations drilled. As will be brought out more, fully hereinbelow, muds which inherently form thick cakes on the walls of the hole lose an undesirable amount of water to the formations being drilled. I have found that highly viscous muds may lose water to the formations even more rapidly than thin muds, depending on their filtration characteristics. Furthermore, the deposition of a very thick or hard cake upon the wall of the hole is undesirable as it may interfere seriously with the entrance or withdrawal of the drilling tools. Thus the ideal mud should permit very little if any loss of water to formation, and should deposit only a relatively thin mud cake on the walls of the hole.

As as been mentioned hereinabove, the most important physical characteristic of a drilling mud is its ability to form a thin impervious cake on the walls of the hole thereby sealing formations against infiltration of water. The terms cake-forming and water-loss properties, sealing properties and, as will be brought out hereinbelow, filtration characteristics or filter rate are used synonymously throughout this specification to denote this characteristic.

As the result of extensive research, I have discovered that a measure of the tendency for a mud to lose water to the formations being drilled and to form a thin impervious cake upon the wall of the hole can be obtained by means of a simple filtration test to be described hereinbelow. In this test the cake-forming properties of the mud are correlated with the ease with which water can be filtered from the mud through a permeable membrane. In fact, I have found that the sealing properties of the mud are almost entirely dependent upon the character of the mud-cake formed when the latter is pressed against a membrane or filter permeable to water and are very largely independent of the character of the membrane or filter employed. As a consequence, the filtration rate of a mud becomes of prime importance in determining the'quality of the mud.

In testing the relative sealing properties of a mud, samples of the actual formation concerned may be employed as the permeable membrane in the filtration test.

The test measurements consist in determining the total volume of filtrate water obtained du n the first hour of pressure filtration, the average rate of filtration during the last half of this hour, and the thickness and texture of the mud filter cake formed during the hour of filtration. Numerous correlations between such tests and actual drilling experience with the same muds have shown that the muds yielding a total filtrate of less than 30 ml. in an hours filtration period at a temperature of 80 F. when using a 600 ml. sampleunder a pressure of 100 lbs. per square inch,

are usually very satisfactory. On the other hand.

muds yielding a total filtrate in excess of 45 ml. under similar circumstances, or a filtration rate of from 25 to 30 ml. per hour during the second half hour of filtration, have been found dangerous to use, particularly when drilling through formations which are readily softened by penetration of water, as cave-ins are liable to occur. Under some circumstances, particularly when drilling surface formations or formations of moderate depth, the permissible maximum filtration rate of the mud above which it becomes dangerous to use may approach approximately 55 ml. under the above circumstances. A mud which is satisfactory for drilling operations will under the conditions of this test, deposit a filter cake of not over one-quarter inch in thickness and of a soft, plastic or gelatinous texture, whereas muds exhibiting unsatisfactory filter rate tend to deposit a thick, tough mud cake. Normally, as has already been mentioned hereinabove, muds possessing acceptable filtering characteristics form good mud cakes and, therefore, in practice only the filtering rate is ordinarily observed.

From the foregoing, it may be concluded that in preparing 'or treating a drilling mud in order to endow it with properties Which will tend to insure satisfactory performance in the field, it is desirable that the treated mud when tested as above described. yield a total filtrate of not over 55 ml. in the first hour of filtration, and that the deposited cake be preferably less than one-quarter inch in thickness and preferably a soft gelatinous texture.

As has already been mentioned hereinabove, a mud in order to be usable, must be capable of being readily and easily circulated by means of a pump such as is ordinarily employed for the purpose in the field. From a practical standpoint, it has been found that within certain limits the more readily the mud can be circulated, the faster will drilling proceed. On the basis of a large number of experiments, it has been determined that for most operations, the viscosity of the mud should be less than 55 seconds as determined by.

the Marsh funnel viscometer when employing the 500 ml. in and 500 ml. out method. It has been observed that muds having funnel viscosities in excess of 55 seconds give rise to impaired circulation rates and increase the danger of gas cutting. The data obtained with the funnel viscometer are empirical and the prior history of the mud will influence greatly the results obtained. For example, in one case it was found that a sample of mud had an indicated funnel viscosity of approximately 45 seconds immediately after being taken from a ditch where it Was flowing very slowly whereas a viscosity of 30 seconds was obtained immediately after agitation. Funnel viscosity determinations should, therefore. be made on samples that have been thoroughly agitated or in rapid motion immediately before the tests are started. Throughout this specification and the claims, wherever the terms viscosity, Marsh viscosity, apparent viscosity or funnel viscosity are employed, they relate to the viscosity as determined by means of the above test, a description of which can be found in an article by H. N. Marsh, entitled Properties and treatment of rotary mud, appearing in the Transactions of the A. P. I. M. E. Petroleum Development and Technology, pages 236 et $4211., in 1931.

Furthermore, I have found that when the viscosity of a mud is sufiiciently low to permit it to be readily circulated and the filtration rate is viscosity and the cake-forming properties of the mud.

It is an additional object of my invention to provide for a combination treatment of muds comprising the addition of one or more chemicals which will control the viscosity of the mud without acceptably altering its cake-forming properties and a second chemical or combination of chemicals which will control the cake-forming properties of the mud without acceptably controlling its viscosity, such combination treatment not materially altering the specific gravity of the mud.

It is also an object of my invention to provide for the chemical pretreatment of mud in order to render it immune to the effects of subsequent contamination with cement or similar materials thereby providing for retaining the mud at all times in excellent condition in terms of the desirable properties enumerated hereinabove.

I have discovered that by a suitable choice of chemical treatment, not only can the viscosity of a mud, and particularly of a contaminated mud, be controlled, but the cake-forming and waterloss properties of the mud, as measured by the filtration rate, can also simultaneously be regulated and maintained at a high quality. It has further been determined that controlling theviscosity of a mud, and especially of a cement-cut mud, does not necessarily control the filtration rate of the mud. In fact, I have discovered that, depending on the effect of any particular compound upon the performance characteristics of a given mud, chemical reagents may be divided into five groups, namely: (1) those which have little or no effect on the performance characteristics, (2) those which have a deleterious effect, (3) those which will control the viscosity but will not lower the filtration rate to a desirable value, l) those which will control the filtration rate but will not lower the viscosity to a desirable value, and (5) those which will simultaneously control both the filtration rate and the viscosity of a mud to an acceptable extent.

I have found that it is desirable in practicing this invention, to improve the performance characteristics of a mud, not to employ an amount of chemical in excess of the minimum amount necessary to obtain the desired performance characteristics. If the reagent exceeds this minimum amount in any great excess, the mud Will be deleteriously affected. Therefore, in making the above classification, it is considered that the chemicals are added in relatively small proportions, normally, in the amountrequired to react with, or negative the influence of, the contaminating material present. By the application of the above described tests, it may be determined what that necessary amount of any given reagent, or reagents, is for any mud.

Before considering the types of reagents belonging in the various groups, it must first be emphasized that, as might be expected, naturally-occurring clays and the muds prepared from them, vary considerably in character. For example, they diffor in ultimate chemical composition, in amounts and type of colloidal material, and in amounts and type of impurities. Furthermore, the common contaminants which may become included in the mud during its use in drilling operations, namely, calcium hydroxide leached from cement, and gypsum, differ in type, one being a fairly strong base and the other a neutral salt. As a consequence, and in view of the complex character of colloidal dispersions, it is only logical to expect that, in general, the performance characteristics of muds prepared from clays of different origins or even of the same mud contaminated with different materials, will not necessarily be affected in the same manner by the addition of any given chemical. As a matter of fact, it has been found, as will be demonstrated hereinbelow, that the performance characteristics of different muds or of the same mud contaminated with difierent types of materials, are in general affected differently by any given chemical reagent.

In spite of these variations, I have found that certain general rules may be applied to permit of the choice of chemicals to be used and to assist in the classification of chemical compounds into the Various groups defined above, and these general rules are presented below.

It will be recalled that the addition to mud of materials which are relatively insoluble in water, such as barium sulfate, iron oxide, etc., has little or no effect upon performance characteristics. Such reagents, therefore, naturally fall into group (1). agents naturally falling into group (1) comprise those compounds which are insoluble in the aqueous phase of the mud.

Materials, such as calcium hydroxide and mag nes'ium chloride, which willdissolve in water to form polyvalent metallic ions, will exert a harmful effect on the performance characteristics of mud. Reagents of this type, therefore, obviously belong in group (2) as harmful. Normally, the strong mineral acids, such as sulfuric acid and hydrochloric acid, whose neutral calcium salts are soluble to the extent of more than 0.15 gram per grams of water at 10 0., when added alone, also belong in group (2) as harmful.

I have found that the'reagents belonging in groups 3, l and 5, and the use of which form the basis of this invention, comprise those acids whose calcium salts are soluble in water to the extent of less than 0.15 gram per 100 grams of water measured at 10 C. This definition is intended to exclude the various acids of phosphorus from group (2) and include them in groups (3), (4) and (5). It is recognized that under certain specific conditions, complexes of calcium ions, with complex phosphate ions, do not precipitate but these complexes appear to be of such a character that for the purposes of this invention, it may be considered that the complex had a solubility of less than 0.15 gram per 100 grams of water at 10 C. By the term acid, it is meant to include all of those compounds, whether organic or inorganic, which contain a hydrogen atom capable of being replaced by a metallic ion. Such acids include carbonic acid, acids of phos phorus, oxalic acid, pyrogallol, tannioacid, etc.

I have also found that the alkali metal and ammonium, neutral and acid, salts of the aforementioned acids, i. e. the acids the calcium salts of which are soluble in water to the extent of not more than 0.15 gram per 100 grams of water measured at 10 0., are also suitable for treating muds and, therefore, also belong in groups 3, 4 and 5.

sodium pyrophosphate, potassium oxalate, sodium tannate, ammonium carbonate, etc. 1

'Ifhe allocation into groups 3, 4 or ".5 of any particular acid or salt of the classes. enumerated hereinabove in any given case will dependprincipally upon the character of the contaminating or flocculating agent and the classification. can be most easily made, without anyknowledge of And in general, it may be said that the re- Such salts include sodium carbonate, sodium bicarbonate, sodium tetraphosphata'tetra I the mud or the character of the contaminating agent by simply adding a small proportion of the particular reagent, for example 0.1% to 1.0%, to the mud under'cbns'ideratioh and determining the efiect on the viscosity and filtration charact'eristics. The methods employed for making performance-tests have been outlined in detail above. In determining the effect of chemicals on 'a m'ud the procedure employed in the laboratory has been to add the desired amount of the chemical or chemicals to the mud followed by a thorough agitation of the. mixture for one hour prior to the conducting of the performance tests.

Itwill be observed that suchfa procedure "completely eliminates any necessity for making a chemical analysis of the mud and, as a consequence, I have foundit to bethe' most practical method which can be employed intheneld.

However, I have also found that,- in general, virgin muds can be classified into murgrou s on the basis of the calcium and sodiumsalt content of the aq'iieous phaseoi the Ihlidi By the term virgin mud is meant mixture of the clayas it is deiivedfromthe earth with appropriate amount or water slichhi this never having: been used for any purpose; :1 inally; amudcompri'ses a mixture ofabout 70 parts by weight of water and 30 parts of clay rid this is the composition of the rhiids to be considered irl the" following discussicn. By the term used mud is meant a virgin mud which has 'be'en iised either in the held in the drilling ofia tve'll error some-other piirpose. i have foundthat tlie aqiieous ha'ses expressed from certain virgin contain esse'hti'allyho dissolved oalci I salts; t is; Iess thanBO'g'ra'ins per gallon of calcium; expressed as calcium carbohate; Typical of this" class is Wilmington siougnniud wh'icli i's d' 'via'd from Biirby sloiigh iii the vicinity ofWil' in on, California; The aqueousphases-expressed rolh many other virgin ihuds contain dissolved calcium salts in excess of so rains per gallon; F'ybi-ctt1 of this classis Cayama vallyfniid; the clay for which is mined about 20 ninesws't of Mal-ricotta,- California. otner'muds orthis same ty-p are DevilsDen mud, Coali'n'ga Redmud, and niiids der'ivel from c'la-ys niin'edat varioiispoints ih the Mbhave Desert.

Aside from the calcium salt content of the aqueous phase. Ihaifealso observedthat the said hase, depending on the source or the particular clay; may also oblltaih' chlo'ride-saltsg expressed as sodium chlorideto the extentof as much as 500 rains per gallon or venmore. I have round that muds in: which theaexpressedi aqueous phase contains in excess of 300 grains per gallon of sodium chloride are? less amenable to-chemical treatmentito lower: their filter rate than muds of lower sodium! chloride content regardless of whether the .-calciumsalt content of the aqueous phase ishigh or low.v The greater theexcessof sodium chloride: above 300 grains per gallon the less the effect: ofchemical treatment; However, I have found that where it is. practicable to employ such muds ln;-drilling=a,well:and replacing the-Water lostfrm-the:;mu-d with fresh water of low total salt content, the'sodium chloride con tent of the aqueous phasecanbedecreased to a value below 309 grains pergallon and when this has occurred, the; fused mud isthen amenable to chemicaltreatment in thesame manner as virgin muds which have less than 300 grains per gallon of sodium chloride inthe aqueous phase. The aqueous phases in many;samples ot wilmingexcess-of 300 parts per de: while the aqueous ton slough mud contain mil ionor. sodium" chlcr-i phases in'samples of high calcium content n'i'ud vary widely; some containing above and others below 300 grains per gallon of sodium chloride.

Virgin muds in which the aqueous phase con-- .tains ihe'xcess of 30 grains per gallon of calcium; expressed as calcium carbonate, are believed to be fio'cculated to a considerable extent and hence are termed flocculated muds? inthis specificationi However; it is certain that flocculation is far from complete and so it. isriot to be implied from such term that the mud is completely flocculated; V V

Onthe other hand, virgin muds in which the aqueous phase contains less than .30 grains per gallon of'calcium, expressed as calcium carbonate, are termed. non-flocculated muds in this specification. ,By thisterm it is not meant to insinu ate that the mud is completely deflocculated but merely to. denote that; although there may be some flocculation due to the presence of calcium ions; these-calciumions are not present in sum cient quantity to give an appreciable. concentration of calcium salts in the aqueous phase. Further, it should be noted that the classificationof muds into fflocculated and non fiocculat'e'd. is made irrespectiveof the sodium chloride content of the aqueous phase: Used muds are classified on. thezbasis ofth characteristlcslof the virgin muds from which theyweregderivedi In general; it'has'b'een observed that the addition-v of a neutral salt, or mixtures of such salts, selectedfrom the classes mentioned herein'above to either fiocculated .;or non floccul-ated virgin muds; orof usedmuds which have become'con' taminated withneutral salts'of polyvalent metallic ions; such as calcium sulfate, will improve the performance; characteristics of. such muds and bring said characteristics within theelimltssp ci fied hereinabove It-hasbeen found specifically that-a further treatment with a small proportion oi quebracho may still further improve the filter rate over that obtained by the addition of a neutral salt alonei v U g r r Whe e.nQmflQ e il -ie udsb e co a ated-with basic materialsof the type; of, calcium i ri B19. is ereri rman charact ristics of 3 n ei insted m dem be i d byihe e9 Hi lel??? 1 1, @9 9 el ted tr muthe class men ned hereinbeioreo; of anacid salt selected thefila entionegl hereinabove; On the Q E5* ....s R dli h e.. ilh hwfieco e c e eet 9 ..wiih a se a s. f the typ .o ee um. h si ei a re umor bythe ad i ion ofeithr an acidsalt of tho typ mentioned hereor o'i'a of, anacidor acid sa1t with'aneutral'sialt selectedjfrom the classes already mentioned hreinbfor; w

sP emQlQS one ereetie a nli a and ofi the process or this; invention as ap: 21 l iniieeeulei d-gahd n -i c u the following tabulated data; are presented. The aqueous phases of the muds treated contained originally less than three hundred parts p'er mil lion of sodium chloride; c, V

In passing it shouldfbenotedthat when more than one reagentisemployedin the treatment ofa mud; the order of addition of the reagents may beof importance; For example,- in the treat-- ment of a virgin Gayama Valleyimud it was found that theaddition of sodium carbonatefollo'wed by the; addition of sodium" tetraphosphate in appropriate proportions almost immediately er i fied an m ro em nt i th rerformance char aoteristics of the mud However, when the order of addition was-reversed. several hours'elapsed if after the treatment before the same improvement in the performance charatceristics was noted. In some cases, it has been observed that a certain order of addition will give better performance characteristics than the reverse order of addition. In the foregoing tables, therefore, unless otherwise noted, it will be considered that the chemicals are added in the order in which they are listed, since they give, when added in such order, the most desirable results.

In the practice of this invention in the field, the treating agents may conveniently be added to the circulating mud stream at a point adjacent to the mud pump suction inlet in the mud sump. Thorough admixture of the thus introduced reagents may be assured by rapid recirculation of the mud from the mud sump through a spare slush pump. During treatment mud samples may be taken from the circulating mud stream at frequent intervals and tested in order to determine when the desired degree of treatment has been effected.

The data presented in Tables I and II concern the treatment of cement-contaminated virgin Cayama Valley and used Wilmington slough muds employed as examples of the classes of flocculated and non-fiocculated muds, respectively. A study of the data given in these two tables will disclose the following facts:

(1) The addition of sodium bicarbonate (Experiment 2 in Tables I and II) in an amount approximately equal to the weight of the contaminating cement reduces both the viscosity and the filtration rate of each of the contaminated muds to acceptable values. It will be observed, however, that in the case of the Cayama Valley mud, the performance characteristics are better than those for the original mud before contamination, whereas in the case of the Wilmington slough mud, although the viscosity of the treated mud is somewhat lower than that of the mud before contamination, the filtration rate is slightly poorer but very acceptable.

It should be noted that the addition of sodium bicarbonate to cement-contaminated muds of various origins and in an amount approximately equal to the weight of the contaminating cement has been found effective in the treatment of such cement-contaminated muds to give products having acceptable performance characteristics. The addition of bicarbonates of other alkali metals and of ammonia and mixtures of carbon dioxide and an alkali metal carbonate have also been found effective in a manner similar to the sodium bicarbonate in the treatment of such cement-contaminated muds. Carbon dioxide is also effective.

(2) Sodium carbonate (Experiment 3, Tables I and II) in an amount approximately equal to the weight of the contaminating cement, is effective in lowering the filtration rate to a desirable value but does not appreciably affect the viscosity.

(3) The addition of quebracho and pyrogallol, respectively, to fiocculated virgin muds which are contaminated by cement (Experiments 5 and 8 in Table I) caused a marked reduction in the viscosity of the mud but had little effect upon the filtration rate. On the other hand, the addition of quebracho and pyrogallol, respectively, to the cement-contaminated used Wilmington slough mud, that is to a non-fiocculated mud which has been contaminated by cement, in the amounts specified in the table (Experiments 5 and 7 in Table II) caused a marked reduction not only 12 in the viscosity but also in therfiltration rate of the mud, so much so that the resultant treated contaminated mud was superior in performance characteristics to the original used mud.

As a further example of the fact that a given reagent has a different effect on muds belonging to different classifications, it will be observed from the comparison of Experiment 14 in Table I and Experiment 11 in Table II that casein had little effect on either the viscosity or the filtration rate of the cement-contaminated Cayama Valley mud, that is of a cement-contaminated mud originally partially fiocculated, whereas in the case of a cement-contaminated Wilmington slough mud, the same reagent in the same proportion markedly lowered both the viscosity and the filtration rate and produced a usable mud.

(4) A treatment comprising the addition of a reagent which will lower the filtration rate without acceptably lowering the viscosity (sodium carbonate) and a reagent which will lower the viscosity without acceptably lowering the filtration rate (quebracho or pyrogallol) apparently produces a combined effect thereby giving a mud of acceptable performance characteristics as is illustrated by Experiments 6 and 9 of Table I. In fact, in the examples given, it will be observed that such a "combination treatment resulted in the production of a mud having markedly superior performance characteristics even in comparison with those of the virgin mud.

In illustrating this effect still further, it will be noted that in Experiment 12 of Table I, the addition of a small proportion of caustic soda to quebracho and a subsequent addition of this mix-' ture to the cement-contaminated Cayama Valley mud, that is to a fiocculated virgin mud containing cement, gave a material having essentially the same viscosity but a lower filtration rate than the addition of quebracho alone. (Compare Experiments 5 and 12 of Table I.) Therefore, in Experiment 13 of Table I the addition of sodium carbonate to the mud was followed by the addition of a mixture of quebracho and caustic soda and the resultant mud had a lower filtration rate than that resulting from a similar treatment with omission of the caustic soda. (Compare Experiments l3 and 6, Table I.)

(5) Exemplary of the fact in order to realize the desired improvement in performance characteristics the amount of reagent added must be carefully controlled by means of adequate tests such as those which have been set up in the foregoing specification, it will be observed from a comparison of Experiments 7 and 8 of Table II that the addition of 0.1% of pyrogallol was sufficient to lower the viscosity and filtration rate of the contaminated mud to acceptable values but that the addition of 1.0% of pyrogallol, although still resulting in the production of a mud of desirable viscosity characteristics, caused the filtration to be increased even above that of the cement-contaminated mud.

The data discussed in the immediately preceding paragraphs has concerned cement-contaminated muds such as are encountered in the field when drilling through cement plugs and the reclamation of such muds is a problem of prime importance as has already been mentioned hereinabove. However, it is also a problem of considerable economic significance to condition ordinary drilling muds in order to improve their performance characteristics. It has been mentioned hereinabove that, depending upon the particular source from which the clay is derived,

virgin muds may be more or less contaminated; H

a filtration rate which is short of the best obtainable by continued treatment but which is acceptable whileatgtheesame time limiting the reby means of the principles which havebeenzset;

forth hereinabove, attention isnowIdirected tog the data presented in Tables III; IV; Vand VI;

The data presented; illustrate theiefiectsQu p onl; performance characteristics which; may attend% the addition ofgvarious chemicals andicombina tions of chemicals to;vi rginand used'muds. It; will be observedzfrom the datapresent edin Tablesg III, IV, V and-.VI, and as hasgalready;been pointedg out in the scussions 7 elatin ametreatment; of cement-contaminated muds that, a, given, chemical may have a different effect; uponthe performance characteristics of different muds.

Furthermore, it will be noted that a combinatior treatment in which a chemical capable of lowering the filtration rate but not the viscos' a chemical capable of lowering thewisc not the filtration rate can be used for th production of usable mud from a poor quality virgin or used mud.

When upon-treatment of muds with. sufizlcientg chemicals to bring; the -filtra tion. rate withimthe; desired values, itmay be found that the viscosi-= ties fall below the range of from2'5 to 35 Marsh seconds which is found to bewithin thehmost de -i sirable valu en thisoccurs. the:viscosity; may be increased to bring;itWithin;the'specified range, without detrimental effectupon thevfilter rate, by increasing the ratio of solids to water in; the and this malbeaccomnli hed ,byieither; allowing a reduction of the water in the mud due to losses to formations, and evaporation or by adding solids such as clay or concentrated col loidal material such as bentonite In some cases the chemical treatment employed for impgroyin the filtration rate can be limitedso" as to obtain" their, use. mayg be; inadvisable.

ducadzviscosity. tp az; value within the desirable valuesi" One. factor; which has not been previously mentioned. concerning. the chemical. treatment of muds is based on the fact that in actual commercial usemudsmay. be exposedj to temperatures of as high as 150 F. to 250 F., the temperature depending; principally uponthe location andthe depth at which the drilling is being conducted. It has'beenobserved that many muds which havebeenchemicallvtreated to improve their performance characteristics tend to deteriorate with respecttothese.characteristics upon prolonged exposure to.temperatures-in the neighbforhoodof 200 F. tjo1250i F., or even lower as is the casein drilling; operations. This is apparently due to the factthatthe chemicals added may be hydrolyzedprotherwise affected in such a manner; as; to; alter; their; original effect upon the performancecharacteristicsiof. the mud. It might-l be thought, therefore, that the use of -chemicalsreacting inthis Way would be a bar to their practical application in the chemical treatment of muds, and in those cases where the degradation with rise in temperature is rapid, suchas in the vcase of sodium hexametaphosphate, However, it has been fqundgthaymany chemicals, which apparently only slowly lose their efiectiveness upon exposure to heat, "may be utilized. In such cases it is preferable to add the chemical; to the mud each day, therebymaintaining. a low filtration rate and alowviscosity. The addition of three times as niuch chemical as is required to maintain the desired performance. characteristics over a period-ofgone day-gwill not maintain the performance characteristics over a period of three days. Ofcourse, it is; evident thatwherever it is feasible, it is preferable touse'; chemicals whose effect upomthe. performance characteristics of a mud are not altered by prolonged exposure to elevated temperatures such as may be encountered in the particular zone being drilled, and

ifsuch chemical,V lillgive the desired performance characteristics according to the tests herein disclosed,v sucha chemical is the most desirable.

Team I 'l ihe cha racteristics of a virgin C'ayama Valley mud. entqminaied ith. 1 f" ydr t d. cement and the effect of added chemicals on the echaracterzstzcs;,

' l Filtration" Gravity Expt. Marsh Viscosity, M Rate, in.

Reagent Added, per cent by weight Seconds lggilc pH g ggg 1 0.1% NaHCOztJ; 10.9 102.0

2 1.0% NaHCOa.. 8.8 51.0

3 1.0% N13200: 11. 3 53v 0 4. 0.1%. Q,uebrach0 1 8 102A) 6 1.0% Quebrach 10.3 121. U

6 1.0% NazGQs-l- 10.8 26,!)

7 .l% lyrogall 10.8 10551) 9.", .0% NazGQS-H) 10.3 30. 4 l0 .0%,Qit,r ic, Acid 8-. .0. 100. 0..

11 .0% Oxalic Acid 7. 9 98. 0

l2" .0%?-LQ,i1ebracho+0.2%.Na0H i 10 .7 97. 0 13, .0%1Na2(;10.a+0.1%NaOH+0.5%.Quebracho 11.0. 2 24.3 14 1.0%;Casein. 10.27. 5 86.03

TABLE VI The characteristics of a virgin Ajax mud and the efiect of added chemicals on these characteristics Filtration Test a Marsh Viscosity, Gravlty Rate, in. N o. Reabent Added b Seconds g; pH Extruded/- 60 min.

None 24.0 1 11b. Na4PzO7 15.0 2 1 lb. Na4PzO1+Quebracho 1 12. 5

1 Values obtained by extrapolation.

The foregoing examples are presented in the nature of illustrations of the practical value of the processes of the invention and are not to be construed as limiting the invention in any sense.

I claim:

1. In the art of drilling wells by the employment of a drilling fluid, with liability of contamination of the fluid during the course of drilling, the process comprising, determining the depth where such contamination occurs and starting treatment of the fluid for a substantial period prior to continuation of drilling beyond such depth, with an agent which inhibits or neutralizes the effect of the contaminant.

2. In the art of drilling wells by the employ" ment of a drilling fluid, with liability of contamination of the fluid during the course of drilling, the process comprising, determining the depth where such contamination occurs and starting treatment of the fluid, for a substantial period prior to continuation of drilling beyond such depth, with an agent which inhibits or neutralizes the effect of the contaminant. and thereafter continuing such treatment.

3. In the art of drilling wells through formations by the employment of a drilling fluid, with liability of addition to the fluid of a di-valent ion when the drill penetrates a formation, the proc ess comprising determining the depth where such penetration occurs and starting treatment of the fluid, for a substantial period prior to the continuation of drilling beyond such depth, with an agent which inhibits or neutralizes the forma tion of such di-valent ion.

4. In the art of drilling wells by the employment of a drilling fluid, wherein such drilling is continued after cementing, the process comprising, determining the depth where the drill reaches the cement and starting treatment of the fluid, for a substantial period prior to continuation of drilling beyond such depth, with a cement-neutralizing agent.

5. In the art of drilling wells through formations by the employment of a drilling fluid, with liability of addition to the fluid from a formation of a viscosity-increasing agent, the process comprising, determining the depth where the drill reaches such formation and starting treatment of the fluid, for a substantial period prior to continuation of drilling beyond such depth, with a viscosity-reducing agent.

6. In the process of treatin muds, contaminated at a certain depth in a bore-hole, by means of a chemical treating agent, comprising, determining the depth where such contamination occurs, and adding the treating agent to the mud a substantial period before drilling at such depth is continued.

7. In the process of treating muds, contaminated at a certain depth in a bore-hole, by means of a chemical treating agent, comprising, determining the depth where such contamination occurs, adding the treating agent to the mud a substantial period before drilling at such depth is continued, and continuing the addition of the treating agent to the circulating fluid until such depth is passed.

8. The treatment of cement-contaminated muds withbicarbonates, comprising, determining the depth where such contamination occurs, and adding bicarbonate to the mud stream a substantial period before drilling at such depth is continued.

9. The treatment of drilling fluids during the drilling-out of cement plugs, the process comprising, adding to the circulating fluid, a substantial period before the cement is drilled out, a substance having precipitating action upon the particles of cement.

10. In the process of drilling through cement plugs by the rotary method of drilling involving 50 the use of a circulating drilling mud which is subject to contamination by cement from the cement plug with resultant increase in the filtration rate of said mud, the steps of determining the depth where such contamination occurs and 55 adding to the drilling mud a substantial period prior to drilling through said cement plug, a chemical reagent which immunizes said drilling mud against substantial increase in the filtration rate of said mud.

11. A process according to claim 10, in which the chemical reagent is sodium bicarbonate.

PHILIP H. JONES. 

